Dynamic data link segmentation and reassembly

ABSTRACT

In a Mobile Ad Hoc Network (MANET), Dynamic Data Link Segmentation and Reassembly (SAR) functions perform a large packet to small packet transformation and reassembles packets at a receiving node. The packet size is determined dynamically in response to link quality data for each individual data link. By periodically sharing link quality information with neighbors, the segmentation size and corresponding reassembly can be performed using readily available neighborhood and waveform information.

RELATED APPLICATIONS

This application claims the benefit of the following U.S. ProvisionalPatent Applications, each of which is incorporated by reference hereinin its entirety:

U.S. App. No. 60/976,730 filed on Oct. 1, 2007;

U.S. App. No. 60/976,735 filed on Oct. 1, 2007;

U.S. App. No. 60/976,740 filed on Oct. 1, 2007;

U.S. App. No. 60/976,744 filed on Oct. 1, 2007;

U.S. App. No. 60/976,747 filed on Oct. 1, 2007; and

U.S. App. No. 60/976,748 filed on Oct. 1, 2007.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with support of the United States Governmentunder Contract MDA972-01-9-0022. The United States Government may havecertain rights in the invention.

BACKGROUND

This invention relates to physical layer communications in a Mobile AdHoc Network (MANET), and more particularly to dynamic segmentation andreassembly of data packets in a data link of a MANET. There remains aneed for improved physical layer handling of data in wireless ad hocnetworks, particularly where traffic of varying types and priorities areexchanged over dynamically changing data links.

SUMMARY

In a Mobile Ad Hoc Network (MANET), Dynamic Data Link Segmentation andReassembly (SAR) functions perform a large packet to small packettransformation and reassembles packets at a receiving node. The packetsize is determined dynamically in response to link quality data for eachindividual data link. By periodically sharing link quality informationwith neighbors, the segmentation size and corresponding reassembly canbe performed using readily available neighborhood and waveforminformation.

In one aspect, a method that is disclosed herein includes providing adata item for transmission from a first node to a second node over adata link in an ad hoc wireless network, the data item having a length;determining a link quality of the data link; selecting a transmit modefor the data link according to the link quality, the transmit modeincluding a data rate; determining a payload length for the data linkaccording to the data rate; segmenting the data item into one or moresegments according to the payload length; and transmitting the one ormore segments as one or more packets over the data link.

In one aspect, a device that is disclosed herein includes a data sourcethat provides data; a data link that packetizes data from the datasource into a packet; a radio that provides an air interface to a mobilead hoc network including a link to a neighboring node; and a signalprocessor that prepares the packet for transmission over the airinterface, the signal processor adapted to dynamically segment thepacket into one or more segments according to a data rate for the link.

In one aspect, a computer program product that is disclosed hereinperforms the steps of providing a data item for transmission from afirst node to a second node over a data link in an ad hoc wirelessnetwork; determining a link quality of the data link; selecting atransmit mode for the data link according to the link quality, thetransmit mode including a data rate; determining a payload length forthe data link according to the data rate; segmenting the data item intoone or more segments according to the payload length; and transmittingthe one or more segments as one or more packets over the data link.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and the following detailed description of certainembodiments thereof may be understood by reference to the followingfigures wherein:

FIG. 1 is a block diagram of a Mobile Ad Hoc Network (MANET).

FIG. 2 is a block diagram of a MANET having multiple backhaul accesspoints.

FIG. 3 is a block diagram of a node in a MANET.

FIG. 4 is a flow chart of a process for measuring link quality.

FIG. 5 is a flow chart of a process for dynamic segmentation andreassembly of data.

DETAILED DESCRIPTION

The following description details certain embodiments of a dynamicsegmentation and reassembly technique for use in packetizing data fortransmission over wireless communication links. By tracking link qualitybased on local metrics and/or information shared among nodes in thenetwork, data can be segmented and reassembled dynamically to providemore efficient use of communication links without requiring moreoverhead in individual packet headers. While the invention is describedbelow in relation to Mobile Ad Hoc Networks, it will be understood thatthe principles of the invention may be suitably applied in anyenvironment where link quality and/or transmission modes varydynamically, and information relating to link quality is available tonodes participating in a network.

So-called “infrastructure” networks employ base stations at fixedlocations to form a substantially fixed network infrastructure. The basestations may enable communication among the wireless devices of thenetwork, between a wireless device and another device on anothernetwork, and so on. This general approach is employed, for example, in802.11 or WiFi networks, as well as in cellular telephony networks. Bycontrast, ad hoc wireless communications networks are formed in an adhoc manner among any number of participating nodes that may periodicallyjoin, leave, or move within the ad hoc network. Although such networksdo not belong to any fixed network infrastructure, they may supportconventional network communications such as point-to-point or broadcastcommunications, and may be adapted for use with any of the InternetProtocols (e.g. IPv4, IPv6) or similar, well-established networkingprotocols.

In general, a Mobile Ad Hoc Network (MANET) is an ad hoc wirelessnetwork in which some (or all) of the participating devices—alsoreferred to herein as “nodes”—are mobile. Thus the topography of a MANETmay change not only as nodes enter and leave the network, but as nodesmove relative to one another within the network. As the network topologychanges, communications routes through the network may also vary interms of availability and in terms of quality. While the invention(s)disclosed herein have broad applicability, they may be particularlyuseful in a MANET environment where the context of continuously changingnode-to-node links poses challenges to, and opportunities for,maintaining traffic flow.

FIG. 1 shows a Mobile Ad Hoc Network (MANET) that may be used with thesystems and methods described herein. In general, a MANET 100 mayinclude subscriber devices 102, access points 104, and backhaul accesspoints 108 (for coupling to a core network 110 such as the Internet),and subscriber devices 110, all generally interconnected as shown inFIG. 1. Without limiting the generality of the foregoing, one or more ofthe subscriber devices 102 may be a stationary device 112 that does notmove within the MANET 100. It will be understood that thedevice-to-device links illustrated in FIG. 1 are for purposes ofillustration only, and in no way are intended to limit the nature ornumber of links between devices in the MANET 100, which may be created,removed, and/or modified over time according to any correspondingprotocols followed by the devices within the MANET 100. In general, thelinks among devices within the MANET 100 are wireless links, althoughwired links may optionally be employed in various locations such asbetween the backhaul access point 108 and the core networks 110. Inorder to maintain the MANET 100, typically one or more protocols areshared among the participating devices to control creation, removal, andmodification of individual data links between devices, and to routetraffic and control information among the devices. The term protocol asused herein generally refers to any and all such rules, procedures,and/or algorithms used in maintaining the MANET 100, unless a specificprotocol is explicitly stated or otherwise clear from the context.

Subscriber devices 102 may include any general purpose nodesparticipating in the MANET 100 according to suitable protocols. It willbe understood that while subscriber devices 102 may include terminalnodes that send or receive data, in a MANET 100 as described hereinsubscriber devices 102 may also suitably be employed as intermediatenodes to route traffic to and from other subscriber devices 102. Thus anad hoc network as described herein is generally extensible, and as newsubscriber devices 102 appear within the MANET 100, they may form a partof the MANET 100 fabric that routes traffic among other nodes. Ingeneral, subscriber devices 102 may include any network or computingdevices that include a wireless interface, network protocol stack(s),and the like adapted to participate in the MANET 100. The InternetProtocol may usefully be employed in subscriber devices 102 within theMANET 100 in order to use well-established addressing schemes and thelike. A subscriber device 102 may include without limitation a cellularphone, personal digital assistant, wireless electronic mail client,laptop computer, palmtop computer, desktop computer, video device,digital camera, electrical instrument, sensor, detector, display, mediaplayer, navigation device, smart phone, a wireless networking card, orany other device that might usefully participate in a network. In someembodiments subscriber devices may include a GPS receiver providing aposition and timing reference. In embodiments, each subscriber device102 may be authenticated and/or authorized before being granted accessto the MANET 100.

Access points 104 may be provided to establish a permanent or otherwisegenerally stable infrastructure to the MANET 100. In one embodiment, theaccess points 104 may employ identical network functionality andprotocol stacks as subscriber devices 102. However, an access point 104may have a number of differences related to their dedicated functionwithin the MANET 100. In one aspect, the access points 104 may have noassociated computing device that originates or consumes network traffic.That is, the access points 104 may simply form a fixed mesh ofparticipants in the MANET 100 and relay traffic among other networkparticipants. An access point 104 may also include a physical connectionto a power infrastructure so that it may be physically installed at alocation and operate autonomously without requiring regular maintenancefor battery changes and the like. In another aspect, access points 104may include some minimal supplemental circuitry related to, e.g., statusand diagnostics, or for receiving software updates and the like. Thismay improve continuity of coverage across a physical region wheresubscriber devices 102 may or may not be present with any regularity,and may ensure that wireless network resources are available in adesired area. In embodiments the access point 104 may be of a size andweight making it suitable for mounting and/or concealment in a varietyof locations including indoor and outdoor locations, and includingmounting on walls, floors, ground, ceilings, roofs, utility poles, andso forth.

Each access point 104 may include or utilize a timing reference such asany of the Network Timing Protocols described in RFC 778, RFC 891, RFC956, RFC 958, RFC 1305, RFC 1361, RFC 1769, RFC 2030, and RFC 4330, allpublished by The Internet Engineering Task Force. Each access point mayalso, or instead, include a GPS receiver providing a position and timingreference. In embodiments the wireless access points 104 may have agreater transmit power and/or a greater antenna gain than mobilesubscriber devices 102, thus providing greater physical coverage thansome other devices within the MANET 100.

The MANET 100 may include one or more backhaul access points 108 thatgenerally operate to connect nodes within the MANET 100 to a corenetwork 110 such as the Internet. On one interface, a backhaul accesspoint 108 may have a wireless radio interface, protocol stack(s) andother components of other nodes within the MANET 100. On anotherinterface, the backhaul access point 108 may provide any suitableinterface to the core network 110. The backhaul access point 108 may,for example, be deployed at a fiber access point or the like thatprovides high-speed data capacity Internet traffic. For example andwithout limitation, the fiber access point may include a Gig-E routersite or an OC-3/12 add-drop multiplexer site. In an embodiment thebackhaul access point 108 may include two Gig-E interfaces for backhaulconnections. It will be understood that any number of a variety ofsuitable interfaces for backhaul connections may be usefully employedwith a backhaul access point 108 as described herein.

A backhaul access point 108 may serve multiple access points 104 withinthe MANET 100, and may distribute network load across those accesspoints 104. Alternatively, a single backhaul access point 108 may servea single access point 104. In some embodiments, the number of accesspoints 104 served by a backhaul access point 108 may relate to theamount of intra-MANET traffic and extra-MANET traffic, the nature anddirection of multicast versus unicast data, and so forth. Thisassociation between backhaul access points 108 and access points 104 maychange from time to time depending on the presence of other subscriberdevices 102 within the area, network conditions, and so forth. In somecases an access point 104 may for a time be associated with more thanone backhaul access point.

The core networks 110 may provide access to network resources outsidethe MANET 100. The core networks 114 may connect disparate,geographically remote and/or local instances of the MANET 100 to form asingle network. The core networks 110 may include any and all forms ofIP networks, including LANs, MANs, WANs, and so on. The core networks110 may also or instead include the public Internet. In otherembodiments the core networks 110 may consist exclusively of a singlezone of administrative control, or a number of zones of administrativecontrol, or some combination of an administrative zone and any of theforegoing.

The stationary device 112 may include any subscriber device 102 that,for whatever reason, does not physically move within the MANET 100. Ingeneral, such fixed physical points within the MANET 100 may provideuseful routing alternatives for traffic that can be exploited for loadbalancing, redundancy, and so forth. This may include, for example, afixed desktop computer within the MANET 100.

Details of various MANET 100 protocols—referred to collectively hereinas the MANET Wireless Protocol (MWP)—are provided below. In general, anyof the nodes above that participate in the MANET 100 according to theMWP may include a hardware platform enabling radio software and firmwareupgrades, which may include for example a dedicated or general purposecomputing device, memory, digital signal processors, radio-frequencycomponents, an antenna, and any other suitable hardware and/or softwaresuitable for implementing the MWP in participating nodes.

In embodiments, any of the foregoing devices, such as one of the accesspoints 104, may also include an adapter for other networks such as anEthernet network adapter or equivalent IP network adapter, router, andthe like, so that non-MANET 100 equipment can participate in the MANET100 through the device. It will also be appreciated that, while aconnection to other core networks 110 is shown, this connection isoptional. A MANET 100 (with or without fixed access points 104) may bemaintained independently without connections to any other networks, andmay be usefully employed for the sole purpose of trafficking data amongsubscriber devices 102.

FIG. 2 is a block diagram of a MANET having multiple backhaul accesspoints. In general, the MANET 100 may include subscriber devices 102(not shown), access points 104, and backhaul access points 108 forconnecting to core networks 110, and an edge router 202 that facilitatesrouting between the MANET 100 and the core networks 110.

The edge router 202 may include any devices or systems for maintainingconnectivity between the MANET 100 and the core networks 110, and mayfurther support or enhance network activity within the MANET 100. Forexample, the edge router 202 may include an industry standard and/orproprietary Address Resolution Protocol server, an application server, aVirtual Private Network server, a Network Address Translation server, afirewall, a Domain Name System server, a Dynamic Host ConfigurationProtocol server, and/or an Operations, Administration, Maintenance andProvisioning server, as well as any combination of the foregoing. Thesevarious components may be integrated into the edge router 202, or may beprovided as separate (physical and/or logical) systems that supportoperation of the edge router 202. These supporting systems may ingeneral support operations such as broadband Internet connectivitywithin the MANET 100 and the like, broadcast communications crossingbetween the MANET 100 and the core networks 110, and so forth, as wellas the use of multiple backhaul access points 108 to efficiently routeinter-MANET traffic among subscriber devices 102.

FIG. 3 is a block diagram of a node in a MANET. The node may be any ofthe devices described above, such as a subscriber device 102, accesspoint 104, or backhaul access point. In general the node 300 may includedata sources 302, a data link 304, a signal processor 306, a radio 308,data queues 310, routing information 312, and neighborhood information314. It will be understood that the following description is general innature, and that numerous arrangements of processing, storage, and radiofrequency hardware may be suitably employed to similar affect. Thisdescription is intended to outline certain operations of a MANET noderelevant to the systems and methods described herein, and in no waylimits the invention to the specific architecture shown in FIG. 3.

The data sources 302 may include any applications or other hardwareand/or software associated with the node 300. This may include, forexample, programs running on a laptop or other portable computingdevice, a web server or client, a multimedia input and/or output sourcessuch as a digital camera or video, and so forth. More generally anydevice, sensor, detector, or the like that might send or receive datamay operate as a data source 302 in the node 300. It will be furtherunderstood that some nodes such as access points 104 may not haveindependent data sources 302, and may function exclusively as MANET 100network elements that relay data among other nodes and/or providenetwork stability as generally described above.

The data link 304 may include hardware and/or software implementing datalink layer functionality such as neighbor management, segmentation andreassembly of data packets, Quality of Service (QoS) management, dataqueue servicing, channel access, adaptive data rates, and any othersuitable data link functions. In general, the data link 304 controlsparticipation of the data sources 302, and more generally the node 300,in a MANET. It will be understood that the data link 304 in FIG. 3 mayimplement any number of lower layer (e.g., physical layer) or higherlayer (e.g., routing, transport, session, presentation, application)protocols from a conventional Open Systems Interconnection (OSI) Model,or any such protocols and related functions may be implemented elsewherewithin the node 300, such as in an IP stack executing on the data source302, or in firmware within the signal processor 306 or radio 308, or inadditional functional blocks not depicted in FIG. 3. For example,routing protocols may be implemented within hardware/software of thedata link 304 in order to ensure that nodes in the MANET 100 shareappropriate routing functions. Thus it will be appreciated that whilethe certain elements discussed herein might suitably be placed withinthe data link layer of a formal protocol stack, the systems and methodsof this disclosure might also or instead be implemented with variationsto a conventional protocol stack, or without any formal protocol stackwhatsoever.

The data link 304 may include a link manager that collects neighborinformation from the data link layer, and may form and maintains theneighborhood information 314 for the node 300. This table may be used toestablish routes to neighbors, and may be updated periodically withinformation from one and two hop neighbors as described further below.The link manager may monitor statistics on all active links for a nodeon a link-by-link basis in order to support link quality calculationsand other functions described herein.

The signal processor 306 may include waveform processing and timingfunctions associated with transceiving data at the node 300. This mayinclude, for example, network timing, time-slot and/or frame-basedwaveform configuration, maintenance of one or more families ofOrthogonal Frequency Division Multiplexing waveform modes (or othertransmit mode waveforms), receiver detection of waveform modes, errorcorrection coding, and so forth. In general, the signal processor 306may be implemented in any suitable combination of digital signalprocessors, field programmable gate arrays, application-specificintegrated circuits, microprocessors, or other general orspecial-purpose computing devices.

In one embodiment, a family of Orthogonal Frequency DivisionMultiplexing (OFDM) waveforms may be employed for adaptive data ratecommunications. The modes of the OFDM waveforms may, for example,include 7.2 MHz Quadrature Phase-Shift Keying (QPSK), 4.8 MHz QPSK, 2.4MHz QPSK, 1.2 MHz QPSK, 1.2 MHz Binary Phase-Shift Keying (BPSK), or thelike. The effective data rate for transmit waveforms may be affected byother parameters such as error correction. In order to facilitateimplementation of an adaptive rate system, the transmit modes may beorganized into an ordered list of monotonically increasing data ratesmatched to correspondingly decreasing signal robustness, thus permittingunique mapping of link quality to transmit mode. In one aspect, theactual waveform mode selected to transmit data on a link may beadaptively selected according to any suitable evaluation of link qualityfor links to neighboring nodes.

The radio 308 in general operates to transmit data from the dataqueue(s) 310, as organized and encoded by the data link 304 and thesignal processor 306 (along with any control information, packet headerinformation, and so forth), over a wireless air interface to other nodesin a MANET, and to perform complementary data reception. The radio 308may include any radio frequency analog circuitry and the like, and maybe coupled to the signal processor 306 which converts data and controlinformation between a digital representation used within the node 300,and an analog representation used in radio frequency communications withother nodes. In embodiments, a low power radio 308 may be employed, suchas where the node 300 is a battery-powered mobile device. In otherembodiments, a high-power radio 308 may be employed, such as where thenode 300 is an access point or backhaul access point connected to afixed power infrastructure. In an embodiment, the radio 308 and signalprocessor 306 provide adaptive data rate coding capable of changingtransmit modes, error correction, and the like according to measuredlink quality.

The data queue(s) 310 may include any data for transmission from thenode 300. This may include, for example, data from the data sources 302,data that is relayed by the node 300 from other nodes in the MANET,and/or control information scheduled for transmission within datapackets from the node 300. The data queue(s) 310 may be organized in anysuitable fashion, and may include a single first-in-first-out queue,multiple queues, prioritized queues, and the like. In one embodiment,the node 300 may include multiple prioritized queues to assist inproviding various service levels, such as for QoS traffic. In general,data in the data queue(s) 310 is delivered according to any suitablequeuing mechanism to the data link 304, signal processor 306, and radio308 for transmission within the MANET.

Routing information 312 such as a routing or forwarding table may beprovided to support routing functions by the node 300. In general, thismay include, for example, a destination address or identifier, a cost ofa path to the destination (using any suitably cost calculation), and anext hop on that path. Other information such as quality of service andother metrics for various routes and links may also be provided for morerefined routing decisions.

Neighborhood information 314 may be maintained in a database, flat file,routing table, or other suitably organized volatile or non-volatilestorage within the node 300. The neighborhood information 314 generallysupports the creation and maintenance of the MANET as well as routingfunctions of each MANET node. Within the MANET, each node may interactwith other nodes to autonomously identify and maintain local networkconnections, shift capacity, dynamically form routes throughout thenetwork, and so on. The routing functions of the node (as supported bythe neighbourhood information 314) may accommodate delay-sensitive (e.g.voice) traffic, delay-tolerant traffic with quality of service (QoS)prioritization, and so on.

The neighborhood information 314 may include an identification ofneighboring nodes along with information relating to those nodes. Thismay include one-hop neighbors (i.e., neighboring nodes in directwireless communication with the node 300), two-hop neighbors (i.e.,neighboring nodes that communicate with the node 300 through only oneother node), or any other nodes or participants within the MANET. In oneaspect, neighborhood information 314 includes link quality informationfor the radio 308, which may be obtained from any combination ofphysical layer and data link data, and may be employed to adapt the datarate of communications according to currently present channelconditions. The neighborhood information may also include QoS data usedto select next hops for QoS data. Other useful information may includebandwidth utilization, node weights, node position (either logical orphysical), and queue latency for each QoS type and/or other prioritytype.

In one aspect, the neighborhood information 314 may be gathered duringperiodic exchanges (such as during control transmissions) withneighboring nodes, which may occur under control of the link manager ofthe data link 304. For example, the node 300 may determine outputbandwidth (i.e., data transmit requirements) for each link that the node300 has with a neighbor, and may transmit this to one-hop neighbors.Similarly, the node 300 may receive output bandwidth from each one-hopneighbor. Using this data, each node 300 may further calculate its owninput bandwidth (i.e., data receive requirements) from each link to aneighboring node, and this information may in turn be exchanged withone-hop neighbors. Following a system-wide exchange with one-hopneighbors, the node 300 (and every other node in the MANET) maycalculate a node weight that represents relative output requirements forthe node 300. For example, the node weight, W, may be calculated as:

$\begin{matrix}{W = \frac{B\; W_{out}}{{B\; W_{out}} + {B\; W_{i\; n}}}} & \left\lbrack {{Eq}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

where BW_(out) is the total output or transmit requirements for eachlink of the node 300, and BW_(in) is the total input or receiverequirements for each link of the node 300. Finally, the node 300 maytransmit the node weight to each neighboring node, and may in turnreceive a node weight from each neighboring node. It will be appreciatedthat the node weight, W, may be further processed for use with otherneighborhood information 314, such as by limiting the value according tothe number of bits used for control information, or by providing asupplemental adjustment to the node weight to further refine control ofrouting or other MANET functions. Sharing of information for maintenanceof the neighborhood information 314 may be controlled, for example, bythe data link 304, which may apply any suitable technique to determinewhen to share information with one hop neighbors. In one aspect, thedata link 304 may transmit data whenever a change is detected in theMANET such as an addition or deletion of a node.

In another aspect, for a MANET that has location-aware nodes 300 (e.g.,using Global Positioning System (GPS) data, signal strength data, and soforth), the neighborhood information 314 may include position data inorder to support location-based routing and the like.

Having described in general terms a MANET that can implement the dynamicsegmentation and reassembly disclosed herein, the description now turnsto a more detailed treatment of an embodiment of systems and methods fordynamic segmentation and reassembly of data. First, an exampleembodiment of link quality measurement is provided, followed by anexample embodiment of the use of this link quality data to segment andreassemble data packets in the physical layer of a MANET radio.

FIG. 4 is a flow chart of a process for measuring link quality. Theprocess 400 may start 402 with a node counting packets received on alink over some predetermined time period such as one second as shown instep 404. Over a corresponding time period, the node may also countpackets sent on the link as shown in step 406. For a Time DivisionMultiple Access (TDMA) system, packet counts may include a count of thenumber of slots received in a TDMA frame.

Each node may then exchange packet count information for each link withneighboring nodes as shown in step 408. This may include, for example,transmitting a count of packets received for each link to eachneighboring node, and receiving from each neighboring node the number ofpackets that they received over each link. This data may be used, forexample, to evaluate missed, dropped, or otherwise lost packets for eachdata link as described below.

Each node may obtain a obtaining a Receive Strength Signal Indicator(RSSI) from a channel, as shown in step 410. This data may be obtained,for example, directly from the radio hardware for the node. It will beunderstood that while an RSSI is a common metric available from radiohardware, any suitable signal strength indicator may also, or instead,be employed.

As shown in step 412, the node may then calculate a link quality foreach link, and the process 400 may return to step 404 where new packetcounts may be obtained. Any suitable calculation may be used tocalculate link quality. For example a ratio of sent-to-received packetsmay be obtained and weighted according to the RSSI. These values providea useful metric that combines the actual, physical signal strength andthe actual, observed packet integrity for a link. Other metrics mayalso, or instead, be employed, such as a signal-to-noise ratio, anaverage signal-to-noise ratio over a predetermined time interval, abit-error rate (prior to any forward error correction), or a simpledropped packet count. The resulting link quality metric(s) may beusefully employed in a number of manners. In one aspect, the linkquality metric(s) may be employed to select a transmit mode (andcorresponding data rate) for each link, thus supporting an adaptive datarate communication channel. In another aspect, link quality informationmay be stored in the neighborhood information for the node, and may beemployed in cost-based route calculations and other routing or networkfunctions. More specifically as it relates to this disclosure, the linkquality metric(s) may be employed to support dynamic segmentation andreassembly of packets as described in greater detail below.

It will be understood that numerous variations to the above process 400are possible without departing from the scope of the invention. Forexample, the rate of change in link quality, distance between nodes,network topology, node movement, or any other metrics that can becaptured by one or more nodes and usefully employed in a link qualitycalculation. Similarly, the order of steps in the process 400 above isnot strictly required, and a step such as calculation of link qualitymay be performed at any regular interval relative to packet counts andchannel measurements. Further, while illustrated as a single process, itwill be understood that any number of link calculations may beperformed, either in serial or in parallel, for some or all of the linksof a node. All such variations that would be apparent to one of ordinaryskill in that art and may be usefully employed in a MANET node areintended to fall within the scope of this disclosure.

FIG. 5 is a flow chart of a process for dynamic segmentation andreassembly of data. In general, the process 500 includes a transmit nodeprocess 502 and a receive node process 504 executed on a node thattransmits the data and a node that receives the data respectively. Theprocess 500 may begin 506 with receiving a packet of data as shown instep 508. The packet may be received from any source within a node,including without limitation one of the data sources of the node asdescribed above, or from one of the data queues of the node used forrelaying unicast or multicast data. The packet may be a layer threepacket including header information such as a source identifier (e.g., alayer 2 address of the node that transmitted the packet), a destinationidentifier (e.g., a layer 2 address of a final destination for thepacket), a type of the packet (e.g., control, application data,invalid), and a type of service for the packet (e.g., a QoS level or thelike for the packet). It will be understood that while the followingdescription relates to packets, which are typically used in an IPnetwork, any data item may be usefully processed as described herein,whether it is received in packetized or other streamed, serial, orsegmented form. For purposes of clarity, it is further noted that a datalink, as used in the following description, refers to an aspect of theair interface for a node, as distinguished from the data link 304described above, which is hardware and/or software implementing layerthree and other functionality of a network protocol stack.

As shown in step 510, a data link for the packet may be evaluated. Inone embodiment, this evaluation may be made with direct reference toinformation in the neighborhood information maintained by the data link,and may simply require retrieving relevant information for the link.Thus, link quality, a transmit mode, and the corresponding payloadlength may be predetermined for the link according to any adaptive datarate protocol employed within the node and/or MANET, and accessed asneeded by the segmentation and reassembly process to facilitateefficient segmentation and reassembly of data. The payload length may bestored with other information for the link, or may be calculated basedon other parameters for the corresponding waveform mode. Relevantinformation may also, or instead, be obtained by direct measurement ofphysical layer characteristics, or by some combination of these. Thus,in general evaluation of the data link may draw on information collectedand maintained by the node during ordinary operation, or may occurconcurrently with receipt of the packet using any available data, orsome combination of these. However performed, the evaluation of the datalink may result in a determination or selection of a payload length forphysical layer packets transmitted by the radio.

As shown in step 512, after determining a payload length for data basedupon an evaluation of a particular data link, the packet received instep 508 may be segmented. In general, this step involves a comparisonof the packet length to the available payload length for the transmitmode of the data link. If the packet length is smaller than the payloadlength, the data in the packet may be transmitted without segmentation.If the packet length is greater than the payload length, any type ofsegmentation may be suitably employed. By way of example, for anadaptive data rate system using four transmit modes having payloadlengths of 1× the network packet length, 0.5× the network packet length,0.25× the network packet length, and 0.125× the network packet length, anetwork packet may be divided into one, two, four, or eight segments. Inone aspect, additional capacity in a transmit mode payload may be filledwith other data, including other segments of other network packetsintended for the same data link or node. It will be appreciated that theabove example is provided by way of illustration and not limitation, andthat there are numerous types of segmentation that may be suitably andusefully implemented in a segmentation and reassembly process asdescribed herein. The applicant has successfully deployed a dynamicsegmentation and reassembly as described herein using as many as twelvedifferent waveform modes.

As shown in step 514, each segment may be encapsulated for communicationto another node in the MANET. This may include the addition of a headercontaining any of the header information from the original packet, aswell as supplemental information to support reassembly. For example, thesegment header may include a transmit mode of the segment, a payloadlength for the segment that specifies a length of a data portion of thepacket (e.g., in bytes), a fragment identifier that specifies a positionof the segment in the original packet, and a last fragment indicator. Astream identifier may be provided that identifies a number of relatedsegments such as segments that share a destination and/or sourceaddress, type of service, and transmit mode. This may be used, forexample, to identify a number of segments belonging to a common stream,but spanning two or more of the network packets received in step 508. Anon-segmented packet may be identified using this header information,such as by setting both the fragment identifier and the last fragmentindicator to a value of one. It will be understood that the segmentationheader information described above is optional. Information such asservice types and transmit modes may also or instead be obtained orinferred from neighborhood information maintained by the receiving nodeas generally described above.

As shown in step 516, a segment may be transmitted to a receiving node.This may include analyzing header information and queuing the segmentfor transmission using any suitable techniques. The segment may then betransmitted over a link of the air interface using a corresponding linkand transmit mode.

As shown in step 518, the segment may be received by a receiving nodeover the corresponding link of the air interface. The segment may thenbe reassembled with other segments into a network packet usingcomplementary operations to those described above. In general, thisreassembly may include using data in the segment header and/orinformation maintained at the receiving node concerning the neighboringnodes.

As shown in step 520, the reassembled network packet may be queued fortransmission to another node in the MANET according to any destinationinformation appended to the data. It will be understood that this stepis optional, and where the data is intended for use at the receivingnode, the network packet may instead be further decoded for use inapplications or the like executing on the receiving node according toany protocol stack(s) on the node. Where the packet is queued forforwarding to another node, the network packet may again be segmented asgenerally described above.

As shown in step 522, the process may end. It will be appreciated thatthe process 500 may be repeated at each hop of a path through a network.Thus in one aspect there is disclosed herein a segmentation andreassembly process that dynamically segments and reassembles data on alink-by-link basis across a multi-hop network route. It will further beappreciated that the order of the steps above may be varied, and thatsteps may be added to, removed from, or modified in the above process500 without departing from the scope of this disclosure. For example,steps that evaluate link quality and assign waveform transmit modes toindividual links may execute independently from the segmentation andreassembly process, and may provide a programming interface, functioncall, object, service, or the like that provides relevant neighborhooddata on an as-needed basis. In addition, a node may support multipledata queues, each of which may execute segmentation and reassemblyprocesses in parallel or serially. It will be further understood thatthe methods and systems described above may be suitably adapted to otherhardware and or software, such as by using directional antennas tomaintain individual data links or by using neighborhood informationinstead of segment header information to control segmentation andreassembly. All such variations that would be apparent to one ofordinary skill in the art are intended to fall within the scope of thisdisclosure.

A wide range of software and hardware platforms may be used to deploythe systems and methods described herein. Generally, the systemcomponents may be realized in hardware, software, or some combination ofthese. The components may be realized in one or more microprocessors,microcontrollers, embedded microcontrollers, programmable digital signalprocessors or other programmable devices, along with internal and/orexternal memory such as read-only memory, programmable read-only memory,electronically erasable programmable read-only memory, random accessmemory, dynamic random access memory, double data rate random accessmemory, Rambus direct random access memory, flash memory, or any othervolatile or non-volatile memory for storing program instructions,program data, and program output or other intermediate or final results.The components may also, or instead, include one or more applicationspecific integrated circuits (ASICs), dedicated semiconductor devices,programmable gate arrays, programmable array logic devices, or any otherdevice that may be configured to process electronic signals.

Any combination of the above circuits and components, whether packageddiscretely, as a chip, as a chip set, or as a die, may be suitablyadapted to use with the systems described herein. It will further beappreciated that the above components may be realized as computerexecutable code created using a structured programming language such asC, an object oriented programming language such as C++, or any otherhigh-level or low-level programming language that may be compiled orinterpreted to run on one of the above devices, as well as heterogeneouscombinations of processors, processor architectures, or combinations ofdifferent hardware and software. Any such combination of hardware andsoftware suitable for use in an ad hoc network as described herein maybe employed without departing from the scope of this disclosure.

Those skilled in the art will recognize, or will be able to ascertainusing no more than routine experimentation, numerous equivalents to thesystems and methods described herein. Such equivalents are considered tofall within the scope of the present invention. Moreover, theembodiments described herein are intended to exemplify the invention andnot to limit it. While the invention is described above in connectionwith certain preferred embodiments, other embodiments may be understoodby those of ordinary skill in the art. All such variations,modifications, extensions, additions, omissions, and the like as wouldbe apparent to one of ordinary skill in the art are intended to fallwithin the scope of this disclosure, which is to be interpreted in thebroadest sense allowable by law.

1. A method comprising: providing a data item for transmission from a first node to a second node over a data link in an ad hoc wireless network, the data item having a length; determining a link quality of the data link; selecting a transmit mode for the data link according to the link quality, the transmit mode including a data rate; determining a payload length for the data link according to the data rate; segmenting the data item into one or more segments according to the payload length; and transmitting the one or more segments as one or more packets over the data link.
 2. The method of claim 1 further comprising measuring a link quality of the data link, and selecting a data rate for the data link based upon the link quality.
 3. The method of claim 2 wherein selecting a data rate further includes selecting one of a plurality of transmit modes for the data link.
 4. The method of claim 2 wherein measuring a link quality includes obtaining a receive signal strength indicator for the data link.
 5. The method of claim 4 further comprising communicating the receive signal strength indicator from the first node to the second node.
 6. The method of claim 2 further comprising counting a number of packets sent from the second node to the first node and transmitting this number from the second node to the first node.
 7. The method of claim 6 wherein measuring a link quality includes comparing the number of packets sent from the second node to a number of packets received from the second node.
 8. The method of claim 1 further comprising selecting the data link from a plurality of available data links between the first node and the second node.
 9. The method of claim 1 further comprising: receiving the one or more packets at the second node; receiving a receive signal strength indicator at the second node, the receive signal strength indicator indicative of a strength of a signal for the data link received at the first node from the second node; receiving a first packet count from the first node, the first packet count indicative of a number of packets received at the first node from the second node over a time period; maintaining a second packet count at the second node, the second packet count indicative of a number of packets transmitted from the second node to the first node over the time period; inferring a segmentation for the one or more packets based upon the first packet count, the second packet count and the receive signal strength indicator; and reassembling the data item based upon the segmentation of the one or more packets.
 10. The method of claim 9 further comprising determining a second receive signal strength indicator according to a strength of a signal for the data link received at the second node from the first node and transmitting the second receive signal strength indicator from the second node to the first node.
 11. The method of claim 1 further comprising, when the payload length is larger than a segment of the data item one of the packets, adding a second segment of a second data item to the payload of the one of the packets.
 12. The method of claim 1 wherein segmenting includes selectively using one, two or four segments for each of the one or more packets according to a length of the data item.
 13. A device comprising: a data source that provides data; a data link that packetizes data from the data source into a packet; a radio that provides an air interface to a mobile ad hoc network including a link to a neighboring node; and a signal processor that prepares the packet for transmission over the air interface, the signal processor adapted to dynamically segment the packet into one or more segments according to a data rate for the link.
 14. The device of claim 13 wherein the air interface includes a plurality of links to a plurality of neighboring nodes.
 15. The device of claim 13 wherein the signal processor modulates the one or more segments with one of a plurality of waveform modes, the one of the plurality of waveform modes selected according to a link quality metric for the link.
 16. The device of claim 15 wherein the link quality metric is determined using a signal strength indicator for the link.
 17. The device of claim 15 wherein the link quality metric is determined using a received packet count and a sent packet count for the link.
 18. A computer program product comprising computer executable code that, when executing on one or more computing devices, performs the steps of: providing a data item for transmission from a first node to a second node over a data link in an ad hoc wireless network; determining a link quality of the data link; selecting a transmit mode for the data link according to the link quality, the transmit mode including a data rate; determining a payload length for the data link according to the data rate; segmenting the data item into one or more segments according to the payload length; and transmitting the one or more segments as one or more packets over the data link.
 19. The computer program product of claim 18 further comprising computer executable code that performs the step of measuring a link quality of the data link, and selecting a data rate for the data link based upon the link quality.
 20. The computer program product of claim 18 wherein selecting a data rate further includes selecting one of a plurality of transmit modes for the data link. 